Process of retaning mineral tanned leather with resorcinol-formaldehyde



United States Patent Douglas K. Severn, Norwich, Conn., assignor to Koppers Company, Inc., a corporation of'Delaware No Drawing. Application June 9, 1954 Serial No. 435,599

12 Claims. (Cl. 8-94.21)

This application is concernedin general with the retannage of leather. More particularly, it is concerned with the retannage of leathers which have been subjected to a mineral tann'age, which is hereinafter spoken of as a pretannage, with such metals as chromium, aluminum, zirconium, titanium, iron, copper, zinc and the like. The invention has particular applicability with reference to the retannage of heavy leathers to yield leathers of greater fullness, m'ellowness, dimensional stability, and in many cases having the property of satisfactory drying under tension Withoutthe necessity of damping and staking to give mel-lown'ess. Additionally, the invention provides a means of increasing the shrink temperature. of leathers having shrink temperatures below 212 F. It is further noted that the hair on hairon hides treated according to the process of this invention have a more silky appearance and tend to have better adherence.

More particularly, the present invention-is concerned with theretanna-ge of mineral pretanned leather utilizing as the retanning agents resorcinol and formaldehyde at a pH in the range of from approx-imately 6.0 to 7.5. An important aspect of the invention resides in the fact that it is now possible to tan with resorcinol and. formaldehyde in a dry tannage, that is, according to the present invention it is not necessary to use relatively dilute solutions Whenutilizing resorcinol and formaldehyde in tanning leathers as heretofore known. Rather, it has been found possible to tan leather utilizing resorcinol and formaldehyde according to the present invention, utilizing only a small amount of Water in excess of that which the hides will absorb. Thus, while the prior art used from-approximately 90 to 125 parts of liquid per 100 parts Wet leather while tanning with resorcinol and formaldehyde it hasnow been found. possible to utilize from to 10 parts 'per 100 parts wet leather.

The present invention comprises a process for the retannage of mineral pro-tanned leather comprising the steps of wetting said leather with water in excess ofthe amount said leather will absorb, draining said. leather, intimately admixing said leather with resorcinol in an amount of approximately 2 to 5 percent based on the rwrung out shaved Weight of said pre-tanned leather, thereafter contacting the admixture of wet leather and resorcinol with formaldehyde in an amount of fromapproximately 1.5 to 3.0.moles per mole. of saidresorcinol, and establishing and maintainingthe. pH of said system in the range of approximately 6.0-7.5 until the supply. of resorcinol and formaldehyde in the liquid present in said system is exhausted.

As used herein the term exhaused is intended to mean that condition which obtains when the addition of concentrated sulfuric acid to a filtered sample of liquid from the tannage drum does not produce a dark red precipitate. As used in this specification and in the appended claims parts and percent means parts by Weight and percent by weight unless otherwise specified.

In general, according to the process of this invention a mineral pre-tanned leather is placed in a tanning drum z; and rinsed with, warm water and the. drum is drained. Thereafter from approximately 2 to 5 percent of the weight of dry leather of resorcinol is added and the leather and resorcinol drummed to intimately admix said leather with said resorcinol that is, for example, for three..quar ters of an hour. Then there is added a mixture of a formaldehydedi berating agent in an amount .of from approximately l.5' to 3.0 moles formaldehydeper mole of resorcinol and an alkali inan amount sufficient to establish the-pH'of the system in the range. approximately. 6.0- 7.5 and preferably in the range. 6.5-7.5. It has been found convenientto add theformalde'hyde and alkaliin an amount;of from approximately 1.5 to 7.5 percent 'by weight. of a mixture of 2 parts by weight paraformaldehyde and 1 part by weight of sodium carbonate. Then the mixture is. drummed for approximately two and ahalf hours after, which time. the drumming is stopped and a 7 check is made of the liquid in the drumfor pH concentration and whether the supply of resorcinol and. form-ab dehyde in. saidliquidis exhausted. If the pH of the liquor is below 6.0 and the supply of resorcinol and formaldehydeis not exhausted there isadded from one to one and one-half percent sodium carbonate and the hides drummed for approximately. one hour. Upon the completion of polymerization the drum is drained and rinsed well at approximately. -140? F. andthe hides fatliquored. with approximately. 5 percent of a suitable oil using the usualfat-liquor procedures.

The. invention is illustrated by, butnot restricted to, the following preferred embodiments:

Example I 360 pounds split shaved weight chrome-tanned hairon S-ounce bellies are added to a tanning dru'mand rinsed and warmed to 130 F. and the drumodrained. There is added 9 pounds of resorcinol and the bel'liesdrummed for 45 minutes. There is then added.l-3.5 pounds of a mixture of 2 parts paraformaldehyde and one part sodium carbonate and the bellies drummed for an. additional two and a half hours. The pH is checked and found to be in the range of 6.5-7.0. A portion of. the. liquid from the drum is filtered and there isadded concentrated sulfuric acid. As no dark red. precipitate forms the supply of resorcinol and formaldehyde is exhausted and the drum is drained. The drum is then rinsed well at l20-l30 and there is added 5. percent of an oil and the regular fat-liquoring procedure followed.

The chrome-tanned stock had a shrink. temperature of F. The retanned stock is capable of withstanding a 5-minute boil in water and the. leather is fuller and more mellow.

Example II 300. pounds split shaved weight alum-tanned hairon lO-ounce croupons are added to a tanning-drum and rinsed and warmed to 105 F. and the drum drained. There is added 9 pounds of resorcinol andthelcroupons drummed for one and.one-half'hours after which there is added'8 pounds of a mixture of 2 parts paraformaldehyde and 1 part sodium carbonate. The croupons are then drummed for 4 hours and a filtered sample of the liquid from the drum tested for exhaustion of the supply of resorcinol and formaldehyde by the addition of concentrated sulfuric acid. As a slight precipitate is formed there is added one and one-half pound sodium carbonate and the pH is then observed to be 6.7. The croupons are drummed for one hour liquid tested for exhaustion of the supply of resorcinol and formaldehyde as above. As no precipitate is observed upon .the addition of concentrated sulfuric acid the supply of resorcinol and formaldehyde is exhausted. The drum is drained, the hides rinsed at l20"v F. and the hides then fat-liquored with 4 percent oil using the regular fat-liquor procedure. 1 i

It is observed that while the alum pre-tanned stock had a shrink temperature of approximately 165-170 F., the retanned stock has a shrink temperature in the range of 200 to 210 F. I

While theforegoing examples illustrate the process of this invention utilizing variousweights of cattle hide bellies and croupons it will be realized that the process of this invention can be utilized with a'wide variety of leathers derived from various animals such as, a for example calfskin and hides from the horse, goatfsheep, alligator, zebra, kangaroo, deer, pig, rabbit and the like. Further, a wide variety of weights of leathers can be utilized by varying the procedure ashereinafter-(described.

Further, it will be realized that, while the foregoing examples illustrate the use'of'paraformaldehyde as a source of formaldehyde, other formaldehyde-liberating agents can be used, in quantities sufiicient to provide the desired amount of formaldehyde. Illustrative of such formaldehyde donors are hexamethyle'netetramine, ethylenedia mine formaldehyde, hydantoin formaldehyde and the like. Mixtures of two or moreof these formaldehyde donors can be utilized to provide formaldehyde in an amount of from approximately 1.5 to 3.0 moles per mole of resorcinol utilized. Additionally, while sodium carbonate has been utilized in the foregoing procedures and is preferred, there can be substituted equivalent quantities of other alkalies which will maintain the system in the pH range of 6.0-7.5 such as for example magnesium oxide, sodium bicarbonate, potassium carbonate, magnesium carbonate, calcium carbonate, calcium oxide, calcium hydroxide, etc. -Mixtures of two or more of these alkalis can be utilized.

In general, utilizing the process of this invention the and a sample of the drum drum times given in Example I can be used for 3-5 ounce stock provided temperatures are held in the range 130- 140 F. For lower temperatures such as for example -110 F., it is preferred to increase the drum times approximately 50-100 percent. For heavy leathers, that is 8-12 ounce stock, it is preferred that the drum times at -140. F. be approximately 50 percent longer than those utilized for 3-5 ounce stock. Additionally, in the retanning of heavy leathers it is preferred that the amount of the admixture of paraformaldehyde and alkali be approximately 2-2 /z percent of the weight of the hides beingretanned. i

Good results are obtained utilizing from 2-5 percent by weight resorcinol and from approximately 3-7 percent with light leathers and from l ir-4% percent for heavy leathers of the mixture of aldehyde and alkali. While good results are obtained in the pH range approximately 6.0-7.5it is preferred that the retannage be carried out at a pH range of 6.5-7.5.

It is to be noted that using the dry tanning process of this invention utilizing resorcinol and formaldehyde at the specified pH range, it is possible to complete the retanning in markedly less time thanheretofore known for resorcinol-formaldehyde tannages. The economic advantage is at once apparent.

While the invention has been described with reference to particular embodiments thereof, it will be understood that in its broadest aspects the invention may be variously embodied within the scope of the invention as set forth herein and in the appended claims.

What is claimed as new is:

1. A process for simultaneously retanning and increasing the shrink temperature of mineral pre-tanned leather comprising the steps of wetting said leather with water in excess of the amount said leather will absorb, draining said leather, intimately admixing said leather with resorcinol in an amount of approximately 2 to 5 percent based an the wrung out leveled weight of said pre-tanned leather, thereafter contacting the admixture of wet leather and resorcinol with formaldehyde in an amount of from approximately 1.5 to 3.0 moles per mole of said resorcinol, and establishing and maintaining the pH of said system in the range 'of approximately 6.0-7.5 until the supply of resorcinol and formaldehyde in the liquid present in said system is exhausted, the resulting retanned leather being capable of withstanding shrinkage in boiling water. f 1

2., A process of claim .1. in which the pH of said system is in the range of 6.5-7.5.

3. A process of claim 1 in which the pH range is estab: lished and maintained by the addition of an alkali.

4. A process of claim 3 in which the alkali is, sodium carbonate.

5. A process of claim 3 in which the alkali nesium oxide.

6. A process of claim 3 in which the alkali is sodium bicarbonate.

7. A process of claim 3 in which the alkali is potassium carbonate.

8. A process for simultaneously retanning and increasing the shrink temperature of mineral pro-tanned leather having shrink temperature below 212 F. comprising the steps of wetting said leather with water in excess of the amount said leather will absorb, draining said leather, intimately admixing said leather with resorcinol in an amount of approximately 2 to 5 percent based on the wrung out leveled weight of said pre-tanned leather, thereafter adding to said admixture approximately 1.5- 7.5 percent based on the dry weight of said pro-tanned. leather of a mixture of 2 parts paraformaldehyde and 1. part of an alkali of such basicity as to establish and maintain the system in the pH range of approximately 6.0-7.5- until the supply of resorcinol and formaldehyde in the. liquid present in the system is exhausted, the resulting rctanned leather being dimensionally stable in boiling water.

9. A process of claim 8 in which the alkali is sodium carbonate.

10. A process of claim 8 in which the alkali is magnesium oxide.

11. A process of claim 8 in which the alkali is sodium bicarbonate.

12. A process of claim 8 in which the alkali is potas-. sium carbonate. 1

is mag- References Cited in the file of this patent UNITED STATES PATENTS Romer Nov. 1, 1921' Great Britain 1907 

1. A PROCESS FOR SIMULTANEOULY RETANNING AND INCREASING THE SHRINK TEMPERATURE OF MINERAL PRE-TANNED LEATHER COMPRISING THE STEPS OF WETTING SAID LEATHER WITH WATER IN EXCESS OF THE AMOUNT SAID LEATHER WILL ABSORB, DRAINING SAID LEATHER, INTIMATELY ADMIXING SAID LEATHER WITH RESORCINOL IN AN AMOUNT OF APPROXIMATELY 2 TO 5 PERCENT BASED ON THE WRUNG OUT LEVELED WEIGHT OF SAID PRE-TANNED LEATHER, THEREAFTER CONTACTING THE ADMIXTURE OF WET LEATHER AND RESORCINOL WITH FORMALDEHYDE IN AN AMOUNT OF FROM APPROXIMATELY 1.5 TO 3.0 MOLES PER MOLE OF SAID RESORCINOL, AND ESTABLISHING AND MAINTAINING THE PH OF SAID SYSTEM IN THE RANGE OF APPROXIMATELY 6.0-7.5 UNTIL THE SUPPLY OF RESORCINOL AND FORMALDEHYDE IN THE LIQUID PRESENT IN SAID SYSTEM IS EXHAUSTED, THE RESULTING RETANNED LEATHER BEING CAPABLE OF WITHSTANDING SHRINKAGE IN BOILING WATER. 